Partial molting synchrony in the giant Malaysian prawn, Macrobrachium rosenbergii: a chemical communication hypothesis

Groups of 50 juvenile specimens ofM. rosenbergii were observed daily for the occurrence of molting for periods up to 50 days. Each animal in a group was physically isolated from the others in one of 50 chambers assembled in a flat chamber array that was immersed in a recirculated bath of fresh water (28 ° C). While an average of 6.4% of the animals molted each day in each of three separate trials, molting occurred in significantly nonrandom peaks and valleys. There was no evidence that peaks in molting frequency occurred at regular intervals, nor were animals of the same size molting synchronously, although weight and molting frequency were significantly correlated. Based on intervals between molts predicted from animal weights, animals molting during a peak molted sooner than animals molting with few others. Molting frequency in a group of animals tended to rise until water was changed, at which time molting frequency dropped significantly. Within each array of animal chambers, animals molted in significant spatial aggregations that coincided with the measured pattern of water flow among chambers in the array. Those spatial aggregations were most pronounced during peaks in molting frequency. These results suggest that some waterborne stimulus, perhaps released by molting animals, is responsible for partial molting synchrony in groups ofM. rosenbergii. The potential advantage of molting synchrony is discussed in connection with the behavioral ecology ofM. rosenbergii.